This invention relates to an image transfer device for an electrostatic copying apparatus comprising a photosensitive drum, and more particularly to apparatus usable with an electrostatic copying apparatus for transferring an image developed on a photosensitive drum onto a sheet of paper being fed, while clamped between a roller and the photosensitive drum.
Used recently in increasing numbers are electrostatic copiers wherein a sheet of paper is clamped between a photosensitive drum and a roller which is applied with voltage so that an image developed on the drum is transferred onto the sheet as the sheet is fed forward. This is because this image transfer method does not generate ozone, and it does not require such a high voltage as is necessary when corona discharge is used to transfer an image from a photosensitive drum onto paper.
As soon as the image is transferred onto it, the sheet must be peeled from the photosensitive drum though it is attracted to the drum under an electrostatic force. The sheet must be quickly fed to a fixing device. To peel the sheet of paper from the drum quickly a tape has long been used. The tape extends in the paper-feeding direction, with both ends fixed, and put in frictional contact with the circumference of one end portion of the drum. The tape is interposed between the drum and one lateral portion of the sheet. The lateral portion of the sheet is not therefore attracted to the drum in spite of the electrostatic force. Thus, as soon as the forward end portion of the sheet comes out of the gap between the drum and the roller, its corner portion, i.e. the forward end part of the lateral portion, falls under its own weight. Then, the other portion of the sheet is gradually peeled from the drum as the sheet is fed.
Interposed between the drum and the roller and fixed at both ends, the tape is pulled in the paper-feeding direction as long as the photosensitive drum is rotating. The tape will eventually be broken and will have to be replaced by a new one. Further, a sheet of paper which is about to leave the drum is likely to tilt about the portion which is still sandwiched between the tape and the photosensitive drum. This results in transfer of a deformed image and may cause jamming of sheets of paper.